Increasingly, vehicle manufacturers outfit their vehicles with a wide array of wireless communications capabilities. Telematics units installed in modern vehicles can wirelessly send both voice and data communications to a variety of recipients. Recipients can be central facilities, such as call centers, that include servers and/or live advisors capable of responding to the telematics unit. Vehicles equipped with telematics units have the ability to monitor and gather a diverse array of data about vehicle-related conditions and send it via the telematics unit. The telematics units can also receive voice and/or data calls from outside callers. For example, during normal operation a telematics unit can receive voice calls from third parties while also standing ready to receive voice and data calls from a call center. However, it is possible that calls originating from third parties may attempt to communicate unwanted or harmful data with the telematics unit. And in those situations, it may be helpful to distinguish between undesirable data calls from third parties and intended calls from the call center.